The Pure Connect database undergoes a process called 'Stream Checking', where all database URLs and external content is checked and updated automatically on a 24 hour basis - every night (at around 4am). The process checks that the radio stream is still streaming and is online, and this helps to ensure the database remains up to date and, of course, your radio stations work.
What can sometimes happen is a radio station stream may fail the stream check process if they happen to be off-line or have changed their streaming URL address at the time of the check. This will result in the station being removed from the Pure Connect database as part of the cleanup process, and if this happens to be a station you listen to then it may not appear in the Pure Connect listings for you to play.
If you find you are missing a station that you normally listen to then you should first check with the station to see if they are still providing an internet streaming service. If they are then get the URL (if it has changed) let us know by contacting us here so we can see if we can get it updated.